Testing Components in Angular Using Jasmine: Part 2, Services

This is the second installment of the series on testing in Angular using Jasmine. In the first part of the tutorial, we wrote basic unit tests for the Pastebin class and the Pastebin component. The tests, which initially failed, were made green later.

Overview

Here is an overview of what we will be working on in the second part of the tutorial.

In this tutorial, we will be:

creating new components and writing more unit tests

writing tests for the component’s UI

writing unit tests for the Pastebin service

testing a component with inputs and outputs

testing a component with routes

Let’s get started!

Adding a Paste (continued)

We were halfway through the process of writing unit tests for the AddPaste component. Here’s where we left off in part one of the series.

As previously mentioned, we won’t be writing rigorous UI tests. Instead, we will write some basic tests for the UI and look for ways to test the component’s logic.

The click action is triggered using the DebugElement.triggerEventHandler() method, which is a part of the Angular testing utilities.

The AddPaste component is essentially about creating new pastes; hence, the component’s template should have a button to create a new paste. Clicking the button should spawn a ‘modal window’ with an id ‘source-modal’ which should stay hidden otherwise. The modal window will be designed using Bootstrap; therefore, you might find lots of CSS classes inside the template.

The template for the add-paste component should look something like this:

The second and third tests do not give any information about the implementation details of the component. Here’s the revised version of add-paste.component.spec.ts.

it('should not display the modal unless the button is clicked', () => {
//source-model is an id for the modal. It shouldn't show up unless create button is clicked
expect(element.innerHTML).not.toContain("source-modal");
//Component's showModal property should be false at the moment
expect(component.showModal).toBeFalsy("Show modal should be initially false");
})
it('should display the modal when `create Paste` is clicked',() => {
let createPasteButton = fixture.debugElement.query(By.css("button"));
//create a spy on the createPaste method
spyOn(component,"createPaste").and.callThrough();
//triggerEventHandler simulates a click event on the button object
createPasteButton.triggerEventHandler('click',null);
//spy checks whether the method was called
expect(component.createPaste).toHaveBeenCalled();
fixture.detectChanges();
expect(component.showModal).toBeTruthy("showModal should now be true");
expect(element.innerHTML).toContain("source-modal");
})

The revised tests are more explicit in that they perfectly describe the component’s logic. Here’s the AddPaste component and its template.

addPaste() is the service’s method for creating new pastes. http.post returns an observable, which is converted into a promise using the toPromise() method. The response is transformed into JSON format, and any runtime exceptions are caught and reported by handleError().

Shouldn’t we write tests for services, you might ask? And my answer is a definite yes. Services, which get injected into Angular components via Dependency Injection(DI), are also prone to errors. Moreover, tests for Angular services are relatively easy. The methods in PastebinService ought to resemble the four CRUD operations, with an additional method to handle errors. The methods are as follows:

handleError()

getPastebin()

addPaste()

updatePaste()

deletePaste()

We’ve implemented the first three methods in the list. Let’s try writing tests for them. Here’s the describe block.

getPastebin returns an array of Pastebin objects. TypeScript’s compile-time type checking can’t be used to verify that the value returned is indeed an array of Pastebin objects. Hence, we’ve used Object.getOwnPropertNames() to ensure that both the objects have the same property names.

Declaring all the variables at the root of the describe block is a good practice for two reasons. The variables will be accessible inside the describe block in which they were declared, and it makes the test more readable.

The above test uses the querySelector() method to assign inputTitle, SelectLanguage and textAreaPaste their respective HTML elements (<input>, <select>, and <textArea>). Next, the values of these elements are replaced by the mockPaste‘s property values. This is equivalent to a user filling out the form via a browser.

element.dispatchEvent(new Event("input")) triggers a new input event to let the template know that the values of the input field have changed. The test expects that the input values should get propagated into the component’s newPaste property.

The extra divs and classes are for the Bootstrap’s modal window. [(ngModel)] is an Angular directive that implements two-way data binding. (click) = "onClose()" and (click) = "onSave()" are examples of event binding techniques used to bind the click event to a method in the component. You can read more about different data binding techniques in Angular’s official Template Syntax Guide.

If you encounter a Template Parse Error,that’s because you haven’t imported the FormsModule into the AppComponent.

component.onSave() is analogous to calling triggerEventHandler() on the Save button element. Since we have added the UI for the button already, calling component.save() sounds more meaningful. The expect statement checks whether any calls were made to the spy. Here’s the final version of the AddPaste component.

If the onSave operation is successful, the component should emit an event signaling the parent component (Pastebin component) to update its view. addPasteSuccess, which is an event property decorated with a @Output decorator, serves this purpose.

//This will be invoked when the child emits addPasteSuccess event
public onAddPaste(newPaste: Pastebin) {
this.pastebin.push(newPaste);
}

If you run into an error, it’s because you haven’t declared the AddPaste component in Pastebin component’s spec file. Wouldn’t it be great if we could declare everything that our tests require in a single place and import that into our tests? To make this happen, we could either import the AppModule into our tests or create a new Module for our tests instead. Create a new file and name it app-testing-module.ts:

Similar to what we did earlier, we will create a new describe block and place the rest of the specs inside it. Nesting describe blocks this way makes the spec file more readable and the existence of a describe function more meaningful.

The nested describe block will have a beforeEach() function where we will initialize two spies, one for the updatePaste() method and the other for the deletePaste() method. Don’t forget to create a mockPaste object since our tests rely on it.

The test assumes that the component has a paste property that accepts input from the parent component. Earlier, we saw an example of how events emitted from the child component can be tested without having to include the host component’s logic into our tests. Similarly, for testing the input properties, it’s easier to do so by setting the property to a mock object and expecting the mock object’s values to show up in the HTML code.

The modal window will have lots of buttons, and it wouldn’t be a bad idea to write a spec to guarantee that the buttons are available in the template.

Being able to view the paste is not enough. The component is also responsible for editing, updating, and deleting a paste. The component should have an editEnabled property, which will be set to true when the user clicks on the Edit paste button.

it('and clicking it should make the paste editable', () => {
component.onEdit();
fixture.detectChanges();
expect(component.editEnabled).toBeTruthy();
//Now it should have a save button
expect(element.innerHTML).toContain('Save');
});

Add editEnabled=true; to the onEdit() method to clear the first expect statement.

The template below uses the ngIf directive to toggle between view mode and edit mode. <ng-container> is a logical container that is used to group multiple elements or nodes.

The obvious difference between this test and the previous ones is the use of the fakeAsync function. fakeAsync is comparable to async because both the functions are used to run tests in an asynchronous test zone. However, fakeAsync makes your look test look more synchronous.

The tick() method replaces fixture.whenStable().then(), and the code is more readable from a developer’s perspective. Don’t forget to import fakeAsync and tick from @angular/core/testing.

Setting Up Routes

To create a routed application, we need a couple more stock components so that we can create simple routes leading to these components. I’ve created an About component and a Contact component so that we can fit them inside a navigation bar. AppComponent will hold the logic for the routes. We will write the tests for routes after we’re finished with them.

Any changes made to the AppModule should also be made to the AppTestingModule. But if you run into a No base href set error while executing the tests, add the following line to your AppTestingModule’s providers array.

routerLink is a directive that is used to bind an HTML element with a route. We’ve used it with the HTML anchor tag here. RouterOutlet is another directive that marks the spot in the template where the router’s view should be displayed.

Testing routes is a bit tricky since it involves more UI interaction. Here’s the test that checks whether the anchor links are working.